Many gas turbine engines include accessory drive gearboxes to drive the various accessory systems needed to operate the engine. As engine and aircraft designs have changed over time, the number of accessories driven by the gearbox has increased. Some of the accessories, to name a few, include electrical power generators, primary gas generator combustor fuel pumps, augmenter fuel pumps, oil pumps, hydraulic pumps and lubrication system scavenge pumps. Typically, during normal engine operation, the gearbox is driven by a tower shaft, which is connected to and driven by a main engine shaft such as the compressor shaft. During the engine start sequence, this loading is reversed and external power is supplied to the gearbox that drives a tower shaft to impart rotation to the compressor. The location of the gearbox can vary depending on engine cycle and application. For moderate to high bypass ratio turbofans used for commercial and transport applications, the gearbox is usually mounted under the core engine cowl onto the engine case. The accessories, in turn, are commonly mounted onto the gearbox housing. For instance, the fuel pump is often bolted to the gearbox on a mounting flange provided at the face of the gearbox.
While effective, the available space between the core engine cowl and the core engine is very limited. In addition to containing the gearbox and the accessories mounted thereon, the space under the core engine cowl also contains engine structural mounts, actuators, plumbing, brackets, controls, fuel lines, air or fluid heat exchangers/coolers and other components. While the number of accessories and components contained under the core engine cowl limit the amount of available space, space is further limited because the gearbox, accessories and components cannot be placed in certain sections of this space due to elevated operating temperatures in those sections. In addition, the operating temperature under the core engine cowl is not evenly distributed. For example, often times the downstream section under the core engine cowl is much hotter than the upstream section. As a result, the gearbox and the accessories are commonly mounted to the upstream section of the engine case in order to prevent exposure to the extreme heat in the downstream section.
Arrangement of the gearbox and accessories under the core engine cowl is also determined by the ease with which the gearbox and accessories can be removed for repair and maintenance. Furthermore, trends for future engine designs suggest that the available space under the core engine cowl will become even more limited. Thus, there is a need to configure the arrangement of the gearbox and accessories in order to maximize use of the limited available space under the core engine cowl.